This invention relates to an electonic musical instrument of a waveform memory read out type wherein a waveform memory device in which the amplitude values at successive sampling points in one period of a desired musical tone waveform are stored in successive addresses is read out by addressing with an accumulated value obtained by repeatedly accumulating, at a predetermined speed, a numerical value corresponding to the tone pitch of a depressed key (hereinafter called a frequency information) and more particularly an electronic musical instrument capable of suitably varying the shape of the waveform read out from the waveform memory device.
In an electronic musical instrument of the waveform memory read out type there is used a frequency information memory device storing frequency informations F corresponding to the tone pitches of respective keys. The frequency information memory device is addressed by key informations representing depressed keys to read out corresponding frequency informations F, and the read out frequency informations F are repeatedly accumulated at a predetermined speed to form progressing accumulated value qF (q=1,2,3 . . . ). This progressing accumulated value is used for sequentially designating the addresses of a waveform memory device in which the amplitude values of successive sampling points which form one period of a desired musical tone waveform have been stored thus sequentially reading out the amplitude values at respective sampling points so as to form a musical tone signal.
For the sake of simplicity, the explanation is done herein with respect to examples of a monophonic type. FIG. 1 is a block diagram showing one example of a prior art electronic musical instrument of a waveform memory read out type which comprises a key switch circuit 1 including a plurality of key switches for respective keys (for example 61 keys) and the output of each key is sent out as a key data KD. A priority circuit 2 connected to receive the key data KD at its input is constructed to produce only one key data KD (key switch output) according to a predetermined order priority (for example, a low tone priority) where a plurality of keys are operated simultaneously, and a key-on signal KON which represents that one of the keys are depressed. A differential circuit 3 is provided to differentiate the build-up portion of a key-on signal KON produced by the priority circuit 2 to produce a differentiated pulse DP. When the differentiated pulse DP produced by the differential circuit 3 is applied to a control terminal 4a, a read-write memory device 4 is written with the key data KD' supplied from the priority circuit 2 whereas in the absence of the differentiated pulse DP, the read-write memory device 4 continuously reads out the key data KD' written therein. There is also provided a frequency information memory device 5 for storing the frequency informations F corresponding to the tone pitches of the respective keys, one information for one pitch. The frequency information memory device 5 is addressed by a key data KD' produced by the read-write memory device 4 to read out corresponding frequency information. An accumulator 6 is connected to the output of the frequency information memory device 5 to sequentially accumulate the frequency information produced by the frequency information memory device 5 at a timing of a clock pulse .phi. and to supply its output to a waveform memory device 7. The amplitude values at successive sampling points of one period of a desired musical tone waveform are stored in respective addresses of the waveform memory device 7 and the addresses thereof are addressed by the progressing accumulated value qF (q=1,2 . . . ) produced by an accumulator 6 so as to read out the amplitude values of the waveform stored in the respective addresses, one after another.
In response to the generation of a key-on signal KON, an envelope waveform generator 8 generates an envelope waveform signal EC that controls such envelopes as an attack, a sustain and a decay. A multiplier 9 is connected between the waveform memory device 7 and the envelope waveform generator 8 to multiply the musical tone waveform read out from the former 7 with the envelope waveform signal EC generated by the latter 8 to apply a volume envelope to the musical tone waveform. A sound system 10 is connected to the output of the multiplier 9 to produce a musical tone waveform applied with the volume envelope as a performance tone.
In the electronic musical instrument of the waveform memory read out type described above, when a key of a keyboard, not shown, is depressed, a key switch of the key switch circuit 1 corresponding to the depressed key is closed to produce a signal "1" which applied to the priority circuit 2 through a corresponding output line. The priority circuit 2 selected a key data KD corresponding to a key switch having the highest order of priority among the key data KD (the outputs of operated key switches) applied thereto so as to produce the selected key data as the key data KD' and a key-on signal KON representing that either one of the keys are now being depressed. The differential circuit 3 differentiates the build-up portion of the key-on signal KON to supply to the control terminal 4a of the read-write memory circuit 4 a differentiated pulse DP having a narrow width and synchronous with the build-up portion. During an interval in which the differentiated pulse DP is supplied from the differential circuit 3, the read-write memory device 4 changes its contents to the key data KD' now being supplied from the priority circuit 2 and stores the key data KD'. As a consequence, the read-write memory device 4 continues to produce the same data KD' until a new key is depressed to produce a new key-on signal KON.
The frequency information memory device 5 is addressed by a key data KD' produced by the read-write memory device 4 whereby a frequency information F from among those as shown in Table 1, for example, and corresponding to the tone pitch of the depressed key is read out from the frequency information memory device 5.
TABLE 1 __________________________________________________________________________ binary digit integer key part fractional part value name F.sub.15 F.sub.14 F.sub.13 F.sub.12 F.sub.11 F.sub.10 F.sub.9 F.sub.8 F.sub.7 F.sub.6 F.sub.5 F.sub.4 F.sub.3 F.sub.2 F.sub.1 in Decimal __________________________________________________________________________ C.sub.2 0 0 0 0 0 1 1 0 1 0 1 1 0 0 1 0.052325 C.sub.3 0 0 0 0 1 1 0 1 0 1 1 0 0 1 0 0.104650 C.sub.4 0 0 0 1 1 0 1 0 1 1 0 0 1 0 1 0.209300 C.sub.5 0 0 1 1 0 1 0 1 1 0 0 1 0 1 0 0.418600 C.sub.6 0 1 1 0 1 0 1 1 0 0 1 0 1 0 0 0.837200 D#.sub.6 0 1 1 1 1 1 1 1 0 1 1 1 0 0 0 0.995600 E.sub.6 1 0 0 0 0 1 1 1 0 0 0 0 0 0 1 1.054808 C.sub.7 1 1 0 1 0 1 1 0 0 1 0 1 0 0 1 1.674400 __________________________________________________________________________
The frequency information F read out from the frequency information memory device 5 and corresponding to the pitch of the depressed key is repeatedly accumulated by an accumulator 6 at a period (i.e. speed) of a clock pulse .phi. to produce an increasing accumulated value qF, where q represents an increasing integer. The increasing accumulated value is used to sequentially address a waveform memory device 7 for sequentially reading out the amplitude values of the waveform stored in the respective addresses, one after another.
The key-on signal KON produced by the priority circuit 2 is also supplied to an envelope waveform generator 8 which generates an envelope waveform signal EC for attack and sustain portions as the key-on signal KON is generated. When the key-on signal KON is extinguished due to key release, an envelope waveform signal EC of the decay portion is generated by the envelope signal generator 8. The envelope waveform signal EC thus produced is applied to a multiplier 9 where it is multiplied with the musical tone waveform read out from the waveform memory device 7 to be imparted with a volume envelope. The musical sound waveform imparted with the volume envelope is converted into a musical tone by a sound system 10.
Where a frequency information F is read out from the frequency information memory device 5 in response to key data KD', the frequency f.sub.T of the musical tone waveform read out from the waveform memory device 7 is expressed by an equation EQU f.sub.T =f.sub.O x F/M
wherein M represents the modulo of the accumulator (i.e. number of addresses of waveform memory) and f.sub.O the frequency of the clock pulse .phi..
The electronic musical instrument of the type descriped above is disclosed in U.S. Pat. Nos. 3,610,806, 3,610,805 and 3,610,799, all dated Oct. 5, 1971.
Since the electronic musical instrument shown in FIG. 1 is constructed such that the frequency information F corresponding to the tone pitch of each key is stored in the frequency information memory device 5, that the stored frequency information is read out when a corresponding key is depressed, that the read out frequency information is sequentially accumulated at a predetermined speed to obtain an increasing accumulated value qF and that the accumulated value qF is used to sequentially read out the amplitude values at successive sampling points in one period of the musical waveform stored in the waveform memory device 7. Accordingly, when the waveform stored in the waveform memory device is determined once the shape of the musical tone waveforms which are read out from the waveform memory device would be always the same so that it is impossible to change the waveform (for example, tone color).
U.S. Pat. No. 3,515,792 issued on June 2, 1970 discloses an improved electronic musical instrument wherein a plurality of waveform memory devices are provided for storing musical tone waveforms having different shapes and the plurality of waveform memory devices are selectively addressed to change the waveform (tone color) of the generated musical tone.
However, the use of a plurality of waveform memory devices not only complicates the construction of the musical instrument but also makes it difficult to store complicated musical tone waveform in the waveform memory device.